1) Field of the Invention
The present invention relates to an object recognition apparatus for a vehicle, made to emit (radiate) a plurality of transmission waves throughout a predetermined angular range in vertical and horizontal (lateral or width) directions of the vehicle for recognizing a reflecting object, such as a preceding vehicle (vehicle ahead), existing in a forward direction of one's vehicle (this vehicle) on the basis of reflected waves thereof, and to an inter-vehicle control apparatus designed to control the distance between oneself and the preceding vehicle recognized, and further to a distance measurement apparatus.
2) Description of the Related Art
So far, as exemplified by Japanese Patent Laid-Open No. 2002-40139, there has been proposed an object recognition apparatus which emits a transmission wave(s), such as optical wave or millimetric wave, in a forward direction of one's vehicle to detect the reflected wave for recognizing an object in the forward direction thereof. This type of apparatus is applicable to, for example, an apparatus made to detect a decrease in spacing from a preceding vehicle or the like and to issue an alarm or an apparatus designed to control the speed of oneself for keeping the inter-vehicle distance with respect to a preceding vehicle, that is, it is utilized for the recognition of a preceding vehicle forming a counterpart of an object of control.
The foregoing object recognition apparatus is designed such that, for example, through the use of a laser radar sensor, a plurality of laser beams are radiated in a forward direction of one's vehicle throughout a predetermined angular range in vertical and horizontal directions of the one's vehicle to recognize a vehicle ahead three-dimensionally on the basis of the reflected light thereof. In this case, if a reflecting object exists at a height or in a range where normal vehicles do not appear, there is a need to make a decision indicative of a non-vehicle (object other than vehicles). Therefore, the identification on a non-vehicle is made through the use of a non-vehicle decision map for the decision between a vehicle and a non-vehicle. As shown in FIG. 25, the non-vehicle decision map is a three-dimensional map in which, for a discrimination between a vehicle and a non-vehicle, light-reception intensity areas on reflected light are set in a state associated with existence regions of a reflecting object with vertical, horizontal and forward directions being taken as X axis, Y axis and Z axis, respectively.
A description will be given hereinbelow of a method for making a discrimination between a vehicle and a non-vehicle through the use of this non-vehicle decision map. First, a decision is made as to which of areas of the non-vehicle decision map the measurement (range) data from a laser radar sensor corresponds to. At this time, if the measurement data pertains to a non-vehicle range, this measurement data is deleted. On the other hand, if the measurement data is involved in an range other than non-vehicle, the measurement data is preserved and is outputted to an inter-vehicle control ECU which takes charge of the implementation of a decision on a preceding vehicle and inter-vehicle control.
As shown in FIG. 25, the non-vehicle decision map is divided into an area in the vicinity of the center thereof, an area around the center area (area in the vehicle of the center thereof) and a lowermost area in the X-axis and Y-axis directions, and the correspondence relationship between a position in the Z-axis direction and a light-reception intensity is set as indicated by (a) to (c) in a state associated with each of these areas. In the X-axis and Y-axis directions, the area in the vicinity of the center shows the correspondence relationship indicated by (b), the area around the center area shows the correspondence relationship indicated by (a), and the lowermost area shows the correspondence relationship indicated by (c).
A description will be given hereinbelow of the correspondence relationship between a position in the Z-axis direction and a light-reception intensity. In the correspondence relationship indicated by (a) to (b), basically, within a predetermined distance range in the Z-axis direction, a predetermined light-reception intensity range is taken as a non-vehicle area, and the range out of that range is taken as a vehicle area. This is because it is considered that a vehicle differs in reflection intensity from a non-vehicle and the reflection intensity of the vehicle is higher than that of the non-vehicle. Moreover, a more appropriate discrimination between a vehicle and a non-vehicle can be made in a manner such that a light-reception intensity for a discrimination between a vehicle and a non-vehicle is set for each reflection object existence area. That is, in an area showing a high possibility of the existence of a vehicle, the measurement data are preserved even if the light-reception intensity is relatively low and, on the other hand, in an area showing a low possibility of the existence of a vehicle, the measurement data are deleted except that the light-reception intensity is relatively high. This enables only the measurement data on a reflecting object showing a high possibility on the existence of a vehicle to be outputted to the inter-vehicle control ECU.
As mentioned above, the conventional object recognition apparatus is designed to successively emit a plurality of laser beams from a laser radar sensor for, in response to the detection of the reflected light thereof, making a decision, through the use of a non-vehicle decision map, as to whether the light-reception intensity of the reflected light corresponds to a vehicle or a non-vehicle.
There is a problem which arises with the decision method of the conventional object recognition apparatus, however, in that there is a possibility of the accuracy of the decision on the vehicle/non-vehicle being sufficiently secured. For example, in a case in which mud or the like sticks to a portion of a vehicle to make it dirty, all the reflected light from the vehicle do not show a high light-reception intensity. That is, measurement data on reflected light having a low light-reception intensity can be included even if the reflecting object is a vehicle. In this case, if a decision is made that the measurement data on the reflected light having a low light-reception intensity corresponds to a non-vehicle and this measurement data is deleted, the measurement data for the reflecting object to be decided as a vehicle becomes in short supply, which can make it difficult to recognize a vehicle with high accuracy.
Furthermore, Japanese Patent Laid-Open No. HEI 11-38141 discloses the scanning on a predetermined two-dimensional area in vertical and horizontal directions. In the case of the scanning on a predetermined two-dimensional area with the emission of a plurality of laser beams (line emission), if a relative large object such as a preceding vehicle exists in front, this object reflects a plurality of laser beams which in turn, are detected by a laser radar sensor. When the laser radar sensor detects the plurality of reflected lights, there is a need to make a discrimination as to whether the reflecting lights are produced by a unitary (same) object or by different objects. That is, in order to correctly recognize each object, there is a need to sort out the reflected lights for each object.
For this reason, in a conventional vehicle object recognition apparatus, positions of the reflecting objects in horizontal directions and distances thereto are calculated on the basis of the reflected light (measurement) data acquired through the line emission, and when the positions of the reflecting objects and the distances thereto are in close conditions, they are presumed as a unitary reflecting object to produce presegment data by unifying them for each emission line. Moreover, the presegment data obtained through the respective line emissions are compared with each other, and when they stand close in position in the vertical direction and distance, they are unified to produce definitive (normal) segment data.
However, in the case of the conventional vehicle object recognition apparatus, since, on the basis of only the position (position in a lateral direction, position in a vertical direction and distance) of a reflecting object, a decision is made as to whether or not the reflecting object is a unitary object, the following problems arise.
For example, even in a case in which a plurality of reflected lights are detected from one preceding vehicle, there is a case in which the intensity of the reflected light from a vehicle body is remote from the sufficiency. Therefore, there is a possibility that the detection of the reflected light from the vehicle body becomes unstable and, in this case, the measurement data on the preceding vehicle becomes unstable.
In addition, in the case of a mere decision on a unitary object on the basis of only the position of the reflecting object, there is a threat of separate objects being taken as a unitary object. For example, in a case in which a stationary thing such as a signboard is at a position above a preceding vehicle or at a side thereof, the preceding vehicle can be recognized as being integrated with the stationary object. In this case, there is a possibility that this object is not correctly recognized as a preceding vehicle because of being different in size from a vehicle.
Moreover, so far, there has been proposed a measurement method based on a signal intensity (strength) of a reflected wave from an object (for example, Japanese Patent Laid-Open No. 2002-22827). According to this measurement method (decision method), for example, in a case in which a pulse wave is emitted to a vehicle existing at a short distance from one's vehicle, a pulse width (deletion pulse width) of a reflected wave is set on the basis of a signal intensity which will develop when normal reflection occurs and is compared with pulse widths of reflected waves detected by the apparatus so that the reflected waves with a pulse width shorter than the deletion pulse width is unemployed for the distance measurement. Thus, if a vehicle is assumed as an object of measurement, the distance measurement is made apart from the detection results on the reflected wave from objects existing at roadsides, or the like, which show relatively low signal intensities.
However, the above-mentioned conventional decision method based on the pulse width of the reflected wave creates the following problems. For example, in a case in which a reflected wave (L) looking like two reflected waves (L1 and L2) overlap is detected as shown in FIG. 23, the pulse width (T) of this reflected wave (L) becomes larger than a deletion pulse width (W) and, hence, the distance to the object is measured on the basis of the detection result on the reflected wave (L).
Such a reflected wave (L) with a large pulse width, which looks like two reflected waves overlap, appears, for example, when a pulse wave emitted is reflected from an object of measurement after passing through spray of water, black smoke or the like and a reflected wave from the object is detected together with a reflected wave from the spray of water or black smoke. Assuming that the reflected wave from the object is the reflected wave (L2), it is required that the pulse width of this reflected wave (L2) and the deletion pulse width (W) be compared in magnitude with each other to make a decision as to whether or not the reflected wave from the object is to be used for the distance measurement.
However, in the case of the conventional decision method, since the decision as to whether or not the reflected wave is to be used for the distance measurement is made on the basis of the relationship in magnitude between the pulse width (T) of the reflected wave (L) and the deletion pulse width (W), even a reflected wave, which cannot provide a sufficient signal intensity, results in having a pulse width corresponding to a high signal intensity due to the environmental influence such as the spray of water or black smoke, and the distance can be calculated on the basis of the resultant reflected wave (L).